Simplify the following expression: $k = \dfrac{tr + r}{4sr} - \dfrac{tr}{4sr}$ You can assume $r,s,t \neq 0$.
Answer: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{tr + r - (tr)}{4sr}$ $k = \dfrac{r}{4sr}$ The numerator and denominator have a common factor of $r$, so we can simplify $k = \dfrac{1}{4s}$